1. Field of the Invention
This invention relates generally to the field of data, video, and voice communications networks, and more particularly optical switches and switching modules, and to a network or network node using an optical switching element having an electro-optic region responsive to an electric field for switching a data communications light beam between an input optical waveguide and one or more output optical waveguides.
2. Description of the Related Art
The increasing amount of data and voice communication has created a great need for improvements in the speed and capacity of the systems used to deliver communication signals. For example, the increasing number of internet users has created a demand for higher volumes of data transfers. The amount of data being communicated by each internet user has been increasing also, creating further demand for communication system capacity. As the amount of data increases, there is also a demand for quicker communication of the data. These increased demands are affecting the data communications companies, telephone companies and cable television companies.
One way to increase the speed and capacity of communication systems is to use fiber optic cables to transfer signals by light beams. A technique called dense wavelength division multiplexing (known as DWDM) has been used to allow many separate signal channels, each at a slightly different wavelength, to be sent on a single fiber optic cable. The use of DWDM allows a great increase in the quantity of data that may be sent through a single fiber optic cable.
A conventional way of routing DWDM optical signals in a network is to use nodes in the network which convert the optical signals to electronic signals using a optical receiver, process and modify the electronic signals for routing, and convert the processed and modified electronic signals back to optical signals using optical transmitters. This type of node is often referred to as o-e-o, meaning that there are conversions in the node from optical to electronic, and back to optical. A problem faced by users of such o-e-o nodes is that the processing and modification of signals in electronic form takes time, and limits the speed at which the node can operate. As the number of DWDM channels flowing through a node increases, the amount of electronic processing and modification inside such an o-e-o node also increases, and requires added electronics which is expensive, heat generating, and space consuming. A further problem faced by users of o-e-o nodes is the expense of such nodes, since many optical detectors are required in each node, and many laser light sources are required in each node, and such detectors and lasers are expensive components. An additional problem faced by users of such an o-e-o node is that optical signals sent to such a node must have a format consistent with the formats used in and supported by such a node. For example, if the particular o-e-o node uses and supports only asynchronous transfer mode (ATM) formatted signals, then an optical signal using the internet protocol (IP) format cannot be sent to and processed by such an o-e-o node. Another problem faced by users of such o-e-o nodes is that fiber optic cables are being installed into existing telephone, cable TV and communication company facilities which are cramped for space, and which do not tolerate being overheated by added electronics. A way to reduce the problem of overheating has been to add air conditioning capacity to existing facilities, but air conditioning equipment requires additional expense, additional amounts of the scarce available space, and additional amounts of electrical power.
Two important needs of modem communications networks are for bandwidth allocation and for service provisioning. Bandwidth allocation refers to the need to change the communications or data transfer capacity, such as the maximum allowable number of voice channels or maximum bit rate, between two nodes in a communications network. Service provisioning refers to the need to provide dedicated communications or data capacity, such as the use of a T3 communications line for a limited time period, to satisfy a particular need, for example a user""s desire to broadcast a combined video and data transmission to a number of sites on a network simultaneously. A network of conventional o-e-o nodes requires significant time to change the configuration of signal pathway connections in all the nodes, thus limiting how fast changes may be made to bandwidth allocation in such networks, and requiring a long setup time for service provisioning in such networks.
A way to overcome some of the problems of o-e-o nodes is to use optical switch elements inside the nodes, so that the optical signals coming into the node are switched into the desired pathways inside the node, and sent out of the node, all without converting the optical signals into electronic signals. The optical switch elements have included micro-electro-mechanical systems (known as MEMS) of miniature moving mirrors that reflect the optical signals into desired pathways. Another optical switch element used in nodes is an optically transparent oil placed in the optical pathway, along with a heater used to create a vapor bubble in the oil, so that the optical signals may be reflected from the surface of the bubble to move the optical signals to the desired pathways. The MEMS optical switch elements may be expensive to manufacture, and wear and breakage of the moving mirrors can result in failure of the optical switch element. The use of oil in a switch element can lead to chemical degradation of the oil as it is heated over a long time period, or leakage of the oil, either of which can result in failure of the optical switch element. A particular problem is believed to occur in a switch which uses oil if the switch is kept in an on condition, with a bubble constantly kept heated for an extended period of time, such as for months or years; in which case the chemical breakdown of the oil is expected and failure of the switch is expected. A way to overcome some of the problems of reliability of MEMS and oil containing optical switch elements is to provide primary optical switch elements and one or more sets of backup secondary optical switch elements of the same type which operate in parallel, and to provide a backup control electronic system for selectively activating the backup secondary optical switch elements in the case of failure of the primary optical switch elements. Such use of primary and secondary optical switch elements increases the size and cost of the node, and the use of such a backup control electronic system increases the size, cost, and waste heat produced by the node. The MEMS optical switch elements require a substantial amount of time to change the optical pathway, since the miniature mirrors must physically change position. The use of oil in an optical switch element requires a substantial amount of time to change the optical pathway, since the heating of oil requires substantial time to create a bubble, and allowing the oil to cool enough to collapse a bubble also requires substantial time. Such delays in changing optical pathways inside a node are disadvantages of the MEMS optical switch element and the optical switch element which uses oil.
Optical switch elements have been suggested that use liquid crystal materials configured to create total internal reflection (known as TIR) optical switch elements. Such liquid crystal materials are known to have thermal instabilities, thus limiting their usefulness as reliable optical switch elements. Optical switches made using such liquid crystal materials are known to have undesirable cross-talk if arrays of such switches are created on a substrate, thus limiting their usefulness, and making them undesirable, since such optical switch elements. Optical switch elements have been suggested using lithium niobate (LiNbO3) as an electro-optic material for waveguides. Such lithium niobate switch elements are known to have high insertion losses and polarization dependent losses, both of which are undesirable properties for optical switch elements. In addition, arrays of switches formed on a substrate using lithium niobate are known to have high crosstalk, which is undesirable for optical switches.
Lead zirconate titanate (known as PLZT) is an electro-optic material that has been used for optical shutters and attenuators.
The use of Clos switches is conventional in optical and electronic switching communications systems.
In one aspect of the present invention, an optical communications network comprises a plurality of fiber optic cables capable of carrying optical communications signals in the form of light beams and a plurality of switching nodes capable of sending and receiving the optical communications signals. Each of the nodes is connected to a predetermined group of the fiber optic cables for switching the optical pathway of the optical communications signals between the predetermined group of fiber optic cables. Each of the switching nodes has a plurality of solid state total internal reflection optical switching elements connected to the fiber optic cables. Each of the solid state total internal reflection optical switching elements have a substantially planar substrate assembly which is electrically insulating and which is not substantially electro-optic. This substantially planar substrate assembly contains substantially planar optical waveguides which are coplanar with and inside the substrate assembly and are capable of guiding the optical pathway of the optical communications signals. At least two of the waveguides meet at a waveguide intersection inside the substrate assembly. Each of the solid state total internal reflection optical switching elements has an electro-optic switching part positioned inside the substrate assembly at the waveguide intersection and is oriented to provide an optical pathway for the optical communications signals to travel through the part and between the waveguides. The switching part has a body material with an electro-optically active region. Activating electrodes are positioned adjacent the switching part to create an optical total internal reflection boundary in the part when a voltage greater than a predetermined switching voltage is applied between the electrodes to create an electric field greater than a predetermined switching electric field inside the part. The electrodes are oriented to align the optical total internal reflection boundary at an angle greater than a predetermined critical angle with respect to the waveguides.
In another aspect of the invention, optical communications switching node includes a plurality of optical inputs to the switching node for receiving optical communications signals and a plurality of optical outputs from the switching node for sending optical communications signals. The optical communications switching node further includes a node controller capable of providing electronic switch selection signals that specify the optical pathway for optical communications signals traveling between the optical inputs and the optical outputs. The electronic switch selection signals exceed a predetermined switching voltage. An optical component is connected to the optical inputs and to the optical outputs, and is responsive to the electronic switch selection signals. The optical component has a plurality of solid state total internal reflection optical switching elements connected. Each of the solid state total internal reflection optical switching elements has a substantially planar substrate assembly which is electrically insulating and which is not substantially electro-optic. The substantially planar substrate assembly contains substantially planar optical waveguides which are coplanar with and inside the substrate assembly and are capable of guiding the optical pathway of the optical communications signals. At least two of the waveguides meet at a waveguide intersection inside the substrate assembly. The solid state total internal reflection optical switching elements also have an electro-optic switching part positioned inside the substrate assembly at the waveguide intersection and oriented to provide an optical pathway for the optical communications signals to travel through the part and between the waveguides. The switching part has a body material with an electro-optically active region. The solid state total internal reflection optical switching elements also have activating electrodes positioned adjacent the switching part to create an optical total internal reflection boundary in the part when a voltage greater than the predetermined switching voltage is applied between the electrodes to create an electric field greater than a predetermined switching electric field inside the part. The electrodes are oriented to align the optical total internal reflection boundary at an angle greater than a predetermined critical angle with respect to the waveguides.
Another aspect of the invention comprises a method of using an optical communications network. In this method, optical communication signals are sent on fiber optic cables connected in a network, and directed to be received by a predetermined destination node connected to the network. Node control signals are provided to specify the optical pathway for the optical communications signals through nodes connected to the fiber optic cables in the network. The optical pathway for the optical communications signals are switched inside a node connected to the network, in response to the node control signals, using a plurality of solid state total internal reflection optical switching elements connected to the fiber optic cables. The solid state total internal reflection optical switching elements have a substantially planar substrate assembly which is electrically insulating and which is not substantially electro-optic. This substantially planar substrate assembly contains substantially planar optical waveguides which are coplanar with and inside the substrate assembly and are capable of guiding the optical pathway of the optical communications signals. At least two of the waveguides meet at a waveguide intersection inside the substrate assembly. The solid state total internal reflection optical switching elements also include an electro-optic switching part positioned inside the substrate assembly at the waveguide intersection and oriented to provide an optical pathway for the optical communications signals to travel through the part and between the waveguides. The switching part has a body material with an electro-optically active region. Activating electrodes are positioned adjacent the switching part to create an optical total internal reflection boundary in the part when a voltage greater than a predetermined switching voltage is applied between the electrodes to create an electric field greater than a predetermined switching electric field inside the part. The electrodes are oriented to align the optical total internal reflection boundary at an angle greater than a predetermined critical angle with respect to the waveguides.
Still another aspect comprises a method of using an optical communications switching node. In this method, optical communications signals are received on a fiber optic cable connected to an input of the node. Node control signals are received that specify the optical pathway for the optical communications signals through the node. The optical pathway for the optical communications signals is switched inside the node, for sending the optical communications signals along an optical pathway to a fiber optic cable connected to a selected output of the node. The selected output is specified by the node control signals. The switching uses a plurality of solid state total internal reflection optical switching elements connected to the fiber optic cables. The solid state total internal reflection optical switching elements have a substantially planar substrate assembly which is electrically insulating and which is not substantially electro-optic. The substantially planar substrate assembly contains substantially planar optical waveguides which are coplanar with and inside the substrate assembly and are capable of guiding the optical pathway of the optical communications signals. At least two of the waveguides meet at a waveguide intersection inside the substrate assembly. The solid state total internal reflection optical switching elements includes an electro-optic switching part positioned inside the substrate assembly at the waveguide intersection and oriented to provide an optical pathway for the optical communications signals to travel through the part and between the waveguides. The switching part has a body material with an electro-optically active region. Activating electrodes are positioned adjacent the switching part to create an optical total internal reflection boundary in the part when a voltage greater than a predetermined switching voltage is applied between the electrodes to create an electric field greater than a predetermined switching electric field inside the part. The electrodes are oriented to align the optical total internal reflection boundary at an angle greater than a predetermined critical angle with respect to the waveguides.
One technical advantage of the technology described below is that high speed optical communications networks may have optical pathways switched quickly and reliably in reduced cost network nodes by the use of solid state TIR optical switch elements made with electro-optic material.
Another technical advantage is that high speed optical communications networks may have network nodes capable of reconfiguring optical pathways quickly in order to allow quick changes in bandwidth allocation in such networks, and in order to allow service provisioning to be provided in such networks with short setup times.
A further technical advantage is that the network nodes have enhanced reliability since they are made using solid state TIR optical switch elements that are thermally stable, have no moving parts to wear out or break, and contain no organic oils that degrade with time or use; including during use in an activated or on condition for extended periods of time, such as for months or years.
Another technical advantage of the technology described below is that the network nodes have reduced cost since the reliability of the solid state TIR optical switching elements reduces the need for expensive multiple layers of redundant backup circuits, and backup control circuits for activating such backup circuits, and the expensive electrical power needed to operate such backup circuits and backup control circuits.
A further technical advantage is that high speed optical communications networks may have optical pathways using a wide variety of optical communications formats by using network nodes having solid state TIR optical switch elements that operate independent of the particular format of the optical communications signals. For example, optical communication signals in having an ATM or IP format may be sent to the optical switch elements, and signals of each format will be switched in the same way, independent of the signal format. The format independence of the switch elements allows an optical network to use new formats for data signals, where such new formats have not been specified at the time that a network node is designed or constructed.
Another technical advantage this technology is that the switching elements used in the network nodes have a low insertion loss, thus reducing the need for optical signal amplification and increasing the number of nodes and distance over which the optical communication signals may propagate without intervening amplification.
A further technical advantage is that the switching elements used in the network nodes do not have polarization dependent losses, thus reducing the need for optical signal amplification and increasing the number of nodes and distance over which the optical communication signals may propagate without intervening amplification.
A further technical advantage is that various embodiments provides polarization independent switching modules as a part of a network node, so that optical communication signals with any of a wide range of polarizations may be reliably switched in the network node.
Another technical advantage is that the switching elements used in the network node use an electro-optic material, PLZT, placed in optically and electrically isolated cavities or regions in a substrate with waveguides so that optical and electrical crosstalk between nearby switching elements is reduced. The reduction of crosstalk is important to improve the performance of the network node to insure that optical communications signals remain private and reliably arrive at designated destinations without contamination by any other optical communications signals passing through the same network node. The reduction of crosstalk also insures that activation of one optical switching element in an array of optical switching elements will not inadvertently activate another nearby optical switching element in the same array.
An additional advantage is that the switching elements used in the network node use a low electrical potential for switching, eliminating the need for expensive, bulky and heat producing high voltage power supplies.